In widespread use today are Christmas light strings formed of Light Emitting Diodes (LED's) connected in electrical series connection operating on rectified AC. While it has been widely thought that LED's would last for thousands and thousands of hours, the reality is that some may fail under certain conditions.
Since the LED's are connected in electrical series connection, the entire light string fails when one light emitting diode fails by opening the electrical connection. One possible solution to this is to provide a shunt across the LED terminals in case of failure. Several types of shunts are possible. One possible shunt is to wind a few turns of oxide coated wire around the two leads of the LED—much like the internal shunt inside an incandescent miniature light bulb. Another possibility is to shunt the LED's in the string with a Zener diode such as disclosed and claimed in U.S. Pat. No. 6,580,182 for incandescent miniature lights.